Basic Semiconductor Theory enjoy the slide

Basic Semiconductor Theory
Contents
 Atomic Theory
 Electrical Material
 Semiconductor Material and their Type
 Intrinsic Semiconductors
 Extrinsic Semiconductors

 Atomic number: number of proton
(), which determines properties
of the element.
 Atomic mass: the summation of
protons and neutrons number (g/mol).

 Valance electron: the number of
electron in the outer shell.
• number of electron distribution on the
shell is given: , where n=1,2,3,...

Materials conductivity Resisstvity Temp.
Cofficient
Examples
Conductor High Low +ve Temp.
Coefficeint
Fe, Al,Cu,Ag,
Insulator Very
Low
Very
High
-Ve Temp.
Coefficeint
Rubber, Glass,
Plastic
Semiconductor Medium Medium -ve Temp.
Coefficeint
Silicon,
Germaninum,
Carbon
Super-
conductor
Very
High
Very Low +ve Temp.
Coefficeint
Mercury and
Aluminium at
Low Temp.

Band Theory of Solids
 Valance Band: which comprises of valence electrons energy
levels.
 Conduction Band: band comprises of free electrons energy
level.
 Band Gap: the energy gap between the valence band and the
conduction.

Semiconductor Materials
 Elemental Semiconductor: Pure Element
 Silicon (si), Germanium (Ge), Carbon (C)
 Compound Semiconductor: Compound (2 or more than 2
elements)
 Gallium Arsenaid (GaAs), Gallium Posphide (GaP),
and Indium Posphide (InP)
Semiconductor Silicon (si) Germanium
(Ge)
Gallium
Arsenaid (GaAs)
Gallium
Posphide (GaP)
Energy Gap 1.06 eV 0.67 eV 1.4 eV 2.2 eV

Types of Semiconductor
 Intrinsic Semiconductor: Pure Crystal structure of
semiconductor materials (i.e. Si, Ge, GaAs).
 Cystal Structure: Repeated and Regular 3D pattern of
elements or compounds.
a) Valance Electron of Silicon b) Crystal Structure of Silicon

Electrons and Holes of Intrinsic Semiconductor
At T=0, there is no any electric charge
The silicon crystal acts as pure insulator
At T>0, thermal energy can break the bond and
it creates the same number of electrons and
holes. At Thermal Energy >= Eg, bond

 Intrinsic Carrier Concentration (): is concentration of free
electrons (-Ve charges) and holes or vacant (+ve charger).
 number of free electrons and holes are equal for Intrisnsic
semiconductor. ,
is band gap energy (eV), T is temperature in kelvin (k),
k is botlzman constant () and B is mterial coefficient.

 Extrinsic (doped) Semiconductor
 The number of electron and hole in an intrinsic semiconductor
are very small, only very small currents are possible.
 Intrinsic semiconductor conductivity can be increase by
adding some impurites (other elements) and this process is
called doping.

 N-type Semiconductors: is an intrinsic semiconductor doped
with pentavalent elements (i.e. phosphorus (P), arsenic (As)).
 N-type: Electron Majority
with minority Holes.
 The phosphorus atom is
called donor impurity with
positive ions ().
 the fifth phosphorus valance
electron is free.

 P-type Semiconductors: is an intrinsic semiconductor doped
with trivalent elements (i.e. boron (B) or Indium (In)).
 P-type: Hole Majority
with Minority of Electron.
 The Boron atom is called
acceptor impurity with
negative ions ().

Current Flow in Semiconductors
 Doping Ratio:
 Low: 1 atom (i.e. Si, Ge) to atoms (i.e. P or B)
 High: 1 atom (i.e. Si, Ge) to 10,000 atoms (i.e. P or B)
 A fundamental relationship between the Electron and Hole
concentration is given as:
, is thermal equilibrium of free electron.
is thermal equilibrium of free holes.
is intrinsic carrier concentration.

Current Flow in Semiconductors
 If the donor concentration () is much larger than the intrinsic
concentration (), we can approximate
, then
 If the acceptor concentration () is much larger than the
intrinsic concentration (), we can approximate
, then

Drift and Diffusion Current
 Drift Current: Flow of charge (carrier) due to external electric
fields (emf).
where, J is total current density (current per Area)
is current density due to majority hole (p-type) carier
is current density due to majority electrons (n-type)
carier
is a constant called hole mobility ()
is a constant of electron mobility ()
E is applied electric field

Drift and Diffusion Current
 Drift Current: Current due to flow of charge from Higher
concentration to Lower concentration.
 The mechanism of transport of charges in a semiconductor
when no electric field is applied called diffusion.
 Diffusion current it only
occurs in semiconductor.

pn junction
 P-N junction is a boundary when p-type and n-type
semiconductor joined together.
Aonde (+Ve)
Cathode (-Ve)
p-type with hole majority
n-type with electron majority

pn junction at zero bias
 What happens when a pn-junction is newly formed?
 First Step: The p-type and n-type semiconductors are joined at
the junction.

 What happens when a pn-junction is newly formed?
 Second Step (Diffusion begins): Those free electrons and
holes which are closest to the junction will recombine. and
this process is called electron-hole recombination.
• N region Loses its electron .... becomes
+vly charged
• P region accepts the electron .... becomes
-vly charged

 Third Step: The depletion region begins.
 After nearly electron diffuse
to the p region, the +Ve ions
protect further electron
movement. the same for p side.
 The Static +Ve and -Ve ions in
the depletion region induce an
static electromagnetic force
(emf). potential barier (Ge=0.3v and Si=0.7v)

Biased pn junction
 Forward Bias: When +Ve terminal of the source ( ) connected
to the Cathode (N-type) and the -Ve terminal to the Anode (P-
type).
1) when, the current
start to increase.
2) Depletion region decreses.
• where, I is Diffusion Current of forward bias
• is saturation current due to minority carrier
• V is Barrier Voltage and is Terminal Voltage

Biased pn junction
 Reverse Bias: When +Ve terminal of the source ( ) connected
to the Anode (P-type) and the -Ve terminal to the Cathode (N-
type).
1) Current is allmost zero
2) Depletion region increse.
3) resistivity is infinite

Reverse Breakdown
 Avalanche Breakdown
• As increases the minority
carriers gets enogh kinetic
energy to be able to break
covalent bonds in atoms .
 Zener Breakdown
• Covalent Bond breakdown
due to exese electric field in
the deplation region .

Diodes and their Application
 Diode is a two-terminal electronic component that only conducts current in one
direction (only in forward bias).
 Forward Bias:
1) Current start to flow.
2) Small (negligible) Resistivity
3) Acts as one way switch (swich “ON”).
 Reverse Bias:
1) Allmost zero flow of current.
2) Infinite Resistivity
3) (swich “OFF”)

Diodes Application
 Half wave rectifier
 In half wave rectification, either the positive or negative half of the
AC wave is passed, while the other half is blocked.

Diodes Application
 Full Wave (Bridge) Rectifier
 A full-wave rectifier converts the whole of the input waveform to one
of constant polarity (positive or negative) at its output.

Diodes Application
 Diode Clipping (Removing) Circuits
 It can be used in voltage limiting applications.

Diodes Application
 Diode Clamper Circuits
 Clamper circuits are the electronic circuits that shift the dc level of the
AC signal.

Diodes Application
 Zener Diode
 special type of diode which allows the current follow to the backward
direction.
 Zener diode is Voltage Regulator (Costant Voltage)

Diodes Application
 Voltage Doubler Diode Circuit
 A voltage doubler is an electronic circuit that produces an output
voltage that is double the input voltage.

Special Purpose of Diodes
 Schottky Diode
 The Schottky Diode is a type of metal-semiconductor diode having a
low forward voltage drop and a very fast switching speed.
 used in a variety of wave shaping, switching and rectification
applications.
 Forward voltage drop is around 0.3V (for Si Diode 0.7V)

 Varactor Diode
 A Varactor diode is a PN junction diode whose capacitance
varies with the change in applied reverse voltage.
 when the reverse voltage changed the deplation layer also
changed, the Varactor diode acts as Capacitor.

 Light-Emitting Diode (LED)
 LED is diode that emits light when biased in the forward
direction of p-n junction.
 Less Power consumption with high Intensity.
 Used In Seven Segment Display
 Optical Communication and etc

Basic Semiconductor Theory enjoy the slide

Basic Semiconductor Theory enjoy the slide

More Related Content

Similar to Basic Semiconductor Theory enjoy the slide

Recently uploaded

Basic Semiconductor Theory enjoy the slide